In semiconductor manufacturing, the production processing equipment used must be controlled such that its variables stay within certain operational limits. These limits can be very narrow and typically vary through out the different steps, stages or phases of the process. Failure to remain within these operational limits during processing can easily cause the loss of, or damage to, the device and/or wafer being processed.
Achieving proper operation of the production equipment typically involves both the initial set-up or configuration of the equipment prior to processing, and the monitoring and control of the equipment during processing. For process chambers, the initial set-up can include chamber matching, which is a method where the performance of the chamber being set up is compared to a data from a set of known good chambers. For monitoring and controlling a process chamber a method of fault detection is typically used. With chamber fault detection, data are monitored and analyzed to identify behavioral deviations from known good (normal) operation of the chamber.
One previous method of chamber matching has been to acquire performance data from the chambers in question and compare to some performance specification. While historically the primarily approach to acquiring data for chamber matching has been to use on-wafer performance (i.e. etch rates, uniformity etc), more recently, due to the large amounts of data provided by newer systems, the approach has been to detect chamber differences without checking on-wafer performance. Eliminating the need for checking on-wafer performance saves both time and costs.
After the process equipment performance has been confirmed (and corrected) by chamber matching, the chamber can be operated using methods to monitor and control the process. Such methods include fault detection where data are monitored from a process tool and analyzed for behavioral deviations. One of the simplest approaches has been to use statistical process control, or SPC, where certain quantities are monitored against upper and lower control limits. Such control limits can range from simple fixed values to those with complex definitions. If a quantity exceeds a certain limit, then the chamber is ‘faulted’ and the processing is halted. This approach ensures that wafers are not mis-processed, and as such, reduces scrap loss, and immediately informs the chamber operators of the problem. In the case of recipe execution for wafer processing, the SPC approach is limited since the processing chamber operates in a series of different regions of its operational space while processing a wafer. The dynamics of the recipe execution (and behavior) is difficult to track with simple SPC methodologies.
Therefore, a need exists for a method, or methods, to provide more accurate way of chamber matching and fault detection.